1. Field of the Invention
The present invention relates to a method and apparatus for radially expanding a container body, to such radially expanded container body and to a container comprising such radially expanded container body.
2. Description of the Related Art
Presently, containers provided with a necked body portion are used for making containers, such as vacuum, pressurized or aerosol containers. Such containers comprise a container body having a necked portion to which necked portion is connected a top closure or cap. Such closure is generally residing within the cylindrical confinement of the container body. The other end of the container body is provided with a bottom end. For such containers having a different surface area at the bottom end and at the cap end, it is possible to use materials of different thickness. For instance, the bottom end has a diameter of about 65 mm and the cap end has a diameter of about 52 mm. At such bottom end the wall thickness may be about 0.18 mm. At the cap end, the cap might have a thickness of about 0.26-0.28 mm or thicker at larger diameters.
For such pressurized container having a necked portion it is traditional to produce the container body for such container by starting from a cylindrical container body produced by forming into a cylindrical shape a rectangular or square sheet of metal of which the abutting or overlapping longitudinal edges are welded together by a longitudinal weld seam.
Subsequently, this cylindrical container body having a longitudinal weld seam is subjected to radial expansion using punch means which are driven through one end of the cylindrical container body and urging radially outwardly the container body into a wider diameter while the punch means progressively are driven through the container body. During the radial expansion by driving the punch means through the cylindrical container body, the body is resting on a reaction table for resisting the driving forces of the punch means exerted on the inner surface of the container body.
The radially expanded container body produced with the traditional method as described above, shows various defects. First, there is a wavy structure over the longitudinal weld seam and over other areas in the outer surface of the cylindrical container body. Second, the end of the container body through which the punch means are driven for radially expanding the container body shows an irregular edge, predominately irregular when this end was provided with a flange intended for connection to the container bottom. Such irregular edge or flange edge at this container end is referred to as earring. This irregular edge may give rise to problems when connecting the bottom end to the container, preferably via the flange of the container body. The irregularities may amount from 0.1 to about 0.5 mm. Third, over the height of the cylindrical container body subjected to radial expansion the wall thickness is not substantially constant and tends to increase onward from the container body end where the radial expansion started.
The irregularities at the container body edge may be removed by cutting resulting in the formation of a substantially regular container body edge. However, such cutting operations are cumbersome and cost raising.